Non-contact IR thermometers are in wide use today. By viewing IR radiation emitted from a surface, a non-contact IR thermometer measures the temperature of that surface from a distance. For example, clinicians in medical clinical settings find IR ear thermometers, which measure the temperature of the tympanic membrane, especially convenient for taking the temperature of a patient.
Manufacturers of IR thermometers spend a considerable amount of time calibrating IR thermometers after final assembly. This calibration typically involves setting calibration constants for each instrument at a given set of instrument and IR calibration target temperatures. For example, it can take hours to “heat soak” a rack of instruments being calibrated after final assembly, in part, because a substantial part of the body of an IR thermometer is often constructed from a thermally insulating material, such as a plastic. Such time consuming calibration procedures can limit the number of instruments that can be produced by a manufacturer and increase capital equipment requirements.
One calibration problem with IR thermometers, particularly those using thermopile IR sensors, is that there are errors in the temperature readings related to the case temperature of the internal IR sensor. The IR sensor case temperature can be affected, for example, by heat flow from the outside environment into the typically plastic outer case or the tip shroud of an IR ear thermometer. Other errors or calibration factors include IR viewing angles through an assembled tip, IR transparency of an outer optical window, and rates of temperature rise for various heat flows and heat flow paths from the environment through the various types of materials present in an assembled IR thermometer. Some such environmental influences, unique to the mechanical and thermal design of each instrument, are taken into account during the typically lengthy calibration of each assembled IR thermometer.
One IR sensor useful for IR thermometer applications includes an internal electronics circuit that can provide some calibration information for the sensor itself. Unfortunately, a small “calibrated” IR sensor part cannot create a calibrated IR thermometer, since a “calibrated” sensor alone does not take into account the actual mechanical and thermal structure of the finally assembled IR thermometer. Building an IR thermometer with such a sensor does not result in a calibrated IR thermometer. Therefore, an IR thermometer built with a “calibrated” IR sensor typically still requires a lengthy final calibration adjustment procedure.
What is needed, therefore, is a tip assembly that can be fully calibrated such that when assembled onto another instrument section, such as an IR thermometer body, no further initial calibration is needed.